Solid state power controllers (SSPCs) are becoming more common for protecting wiring in an electric power distribution system, like a system on an aircraft. These SSPCs act as electronic circuit breakers and replace traditional mechanical, thermally-activated circuit breakers. Aircraft systems using mechanical circuit breakers require circuit breaker panels with hundreds of circuit breakers around the cockpit, thereby requiring many corresponding wires to connect the circuit breakers to various loads in the aircraft and resulting in a great deal of added weight.
Electronic circuit breakers, by contrast, eliminate most of these wires by using a central electronic display to mimic the circuit breaker panel, locating the electronic circuit breakers themselves close to the loads, and using a high current feeder to connect the power source to the electronic circuit breakers and distribute current to the loads. As a result, an operator can simply press soft buttons on the central electronic display to open and close the electronic circuit breakers and check which ones have tripped. This is more convenient than large circuit breaker panels and simplifies the operator interface for the circuit breakers. Moreover, electronic circuit breakers include a microcontroller and/or a digital signal processor (collectively “intelligence”) that can provide many additional functions that are not possible with mechanical circuit breakers, such as arc-fault detection, custom overload control, wire-fault detection, and built-in testing as well as the usual on/off functions.
Electronic circuit breakers, however, operate differently than mechanical circuit breakers because the on/off operation of the electronic circuit breaker is dependent on power reaching the intelligence first before the circuit breaker actually operates. More particularly, a load that is downstream from an electronic circuit breaker will experience a slight delay (e.g., on the order of tens of milliseconds) between the time a power source is connected to the electronic circuit breaker and the time the load senses the power connection because the intelligence needs to first power up and undergo self-testing before it actually turns the circuit breaker on. Mechanical circuit breakers, by contrast, allow the load to respond immediately to power connection because it is normally closed all the time.
This delay does not affect normal operation of the aircraft. However, current aircraft specifications often include a requirement for loads to survive a temporary power interruption for a specified fixed time window (e.g., 200 milliseconds) during fault clearing and bus power transfers. For example, if a generator fails and the loads need to be switched to an alternate power source, the loads are designed to survive the amount of time needed to make the switch. If the load is downstream from an electronic circuit breaker, however, the delay in the circuit breaker caused by waiting for the intelligence to power up will add to the delay caused by the power interruption itself. For example, the intelligence may cause delays by coming out of a reset mode, performing power-up testing, waiting for new commands, and/or determining the circuit breaker state before the power interruption. This may cause the total amount of delay at the load to fall outside the specified time window. In other words, the power interruption at the load will be greater than the power interruption at the power source.
Although this problem may be remedied by simply using a mechanical circuit breaker, which would cause the power interruption at the load to be equal to the power interruption at the source, this is undesirable due to the inherent disadvantages of mechanical circuit breakers noted above.
There is a desire for a system that ensures that a power interruption time period at a load downstream of an electronic circuit breaker will not be greater than a power interruption time at a power source.